Dmytro Firtash, one of Ukraine's most influential oligarchs, appears in Vienna, Austria, April 30, 2015. An Austrian court is due to rule on Thursday on a U.S. request to extradite one of Ukraine's most influential oligarchs, Dmytro Firtash. He was arrested in Vienna in March 2014 at the request of U.S. authorities, which have been investigating him since 2006 for suspected corruption. Firtash has denied the allegations and has been living in Austria after posting 125 million euros in bail. REUTERS/Heinz-Peter Bader TPX IMAGES OF THE DAY

Dmytro Firtash, one of Ukraine's most influential oligarchs, billionaire and industrialist, gestures during a Reuters interview in Vienna, Austria, December 2, 2015. REUTERS/Leonhard Foeger

Dmytro Firtash, one of Ukraine's richest men, (R) and Ukrainian President Viktor Yanukovich take part in an opening ceremony of a new complex for the production of sulfuric acid in Crimea region April 27, 2012. Austria has arrested Ukrainian businessman Firtash at the request of the United States which has been investigating him since 2006, government sources said. The Federal Crime Agency on March 13, 2014 identified the suspect only as Dmitry F., 48, but government sources said it was Firtash. The agency said he was suspected of violating laws on bribery and forming a criminal organisation in the course of foreign business deals. Picture taken April 27, 2012. REUTERS/Mykhailo Markiv (UKRAINE - Tags: POLITICS CRIME LAW ENERGY TPX IMAGES OF THE DAY)

VIENNA, AUSTRIA - APRIL 30: Ukranian businessman Dmytro Firtash (L) is seen during his trial in Vienna, Austria on April 30, 2015. Vienna regional criminal court will decide if he can be extradited to the United States. (Photo by Hasan Tosun/Anadolu Agency/Getty Images)

Dmytro Firtash, one of Ukraine's most influential oligarchs attends a trial on April 30, 2015 in Vienna.The billionaire was recently arrested in Vienna at the request of the FBI and Viennese court is to decide on a US extradition request. AFP PHOTO / SAMUEL KUBANI (Photo credit should read SAMUEL KUBANI/AFP/Getty Images)

Dmytro Firtash, one of Ukraine's richest men, is seen in Kiev June 7, 2012. Austria has arrested Ukrainian businessman Firtash at the request of the United States which has been investigating him since 2006, government sources said. The Federal Crime Agency on March 13, 2014 identified the suspect only as Dmitry F., 48, but government sources said it was Firtash. The agency said he was suspected of violating laws on bribery and forming a criminal organisation in the course of foreign business deals. Picture taken June 7, 2012. REUTERS/Mykhailo Markiv (UKRAINE - Tags: POLITICS CRIME LAW ENERGY)

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The government says that prosecuting Firtash and his co-defendant in the alleged scheme, Andras Knopp, "will disrupt this organized crime group and prevent it from further criminal acts within the United States."

In 2008, according to court records, Manafort's firm was involved with Firtash in a plan to redevelop the Drake Hotel for $850 million. Firtash's company planned to invest more than $100 million, the records say.

One of the other partners working with Manafort on the deal was the former exclusive broker for Fred Trump's properties, Brad Zackson. Fred Trump is the now-deceased father of Donald Trump.

Eventually, documents show, Firtash's investment company transferred $25 million into escrow to further the project.

Also in 2008, according to a State Department cable posted by WikiLeaks, Firtash told U.S. Ambassador William Taylor that he got his start in businesswith the permission of one of Russia's most well-known organized crime bosses, Semion Mogilevich. But Firtash claimed to Taylor that he was forced to deal with such people.

Republican presidential nominee Donald Trump gives a thumbs up as his campaign manager Paul Manafort (C) and daughter Ivanka (R) look on during Trump's walk through at the Republican National Convention in Cleveland, U.S., July 21, 2016. REUTERS/Rick Wilking

Republican U.S. presidential candidate Donald Trump's campaign manager Paul Manafort talks to the media from the Trump family box on the floor of the Republican National Convention in Cleveland, Ohio, U.S. July 18, 2016. REUTERS/Jonathan Ernst

Paul Manafort, senior advisor to Republican U.S. presidential candidate Donald Trump, smiles as he talks with other Trump campaign staff after Trump spoke to supporters following the results of the Indiana state primary, at Trump Tower in Manhattan, New York, U.S., May 3, 2016. REUTERS/Lucas Jackson

UNITED STATES - JULY 20: A man with a security credential takes a selfie at the podium as Donald Trump, flanked by campaign manager Paul Manafort and daughter Ivanka, checks the podium early Thursday afternoon in preparation for accepting the GOP nomination to be President at the 2016 Republican National Convention in Cleveland, Ohio on Wednesday July 20, 2016. (Photo By Bill Clark/CQ Roll Call)

UNITED STATES - JULY 19: Paul Manafort, advisor to Donald Trump, is seen on the floor of the Quicken Loans Arena at the Republican National Convention in Cleveland, Ohio, July 19, 2016. (Photo By Tom Williams/CQ Roll Call)

NA.R.DoleMicCk1.081596.RG.Republican presidential candidate Bob Dole looks up from podium at balloons and television cameras as convention center manager Paul Manafort, at right, points out preparations for tonight's acceptance speech in San Diego, 08/15/96. (Photo by Robert Gauthier/Los Angeles Times via Getty Images)

Firtash was a major backer of Ukraine's Party of Regions, the pro-Russian party for which Manafort worked for many years, according to the federal criminal complaint and another leaked State cable. Manafort's firm made more than $17 million in gross revenue from the party in just two years, according to his recent Foreign Agent Registration Act filing. Another leaked cable said that Manafort's job in 2006 was to give the Party of Regions an "extreme makeover" and "change its image from ... a haven for mobsters into that of a legitimate political party."

In interviews and statements to NBC News, Manafort has said he "never had a business relationship" with Firtash. "There was one occasion where an opportunity was explored. ... Nothing transpired and no business relationship was ever implemented."

The government's 115-page filing came in response to a motion to dismiss by Firtash's lawyers, who say the government has failed to establish that any crime occurred in the U.S.

In a statement to NBC News, Firtash attorney Dan Webb said the government filing makes two accusations that are not part of the federal indictment — that Firtash is connected to Russian organized crime, and that he made bribe payments intended for individuals in the U.S. Webb said there is "no evidence" that Firtash is linked to organized crime, and the accusation that he made bribe payments "is also false, and that is why the government did not include it as well in its own indictment."

The U.S. Attorney's Office for the Northern District of Illinois did not respond to a request for comment.